Synthesis of triarylsulfonium salts

ABSTRACT

A triarylsulfonium salt is prepared in high yield and high purity by a two-step process involving a aryl Grignard reagent reacted with a diarylsulfoxide in a solvent which is a mixture of aliphatic and aromatic hydrocarbons, followed by a second step which is metathesis with ZMF 6 , where Z is a metal or metal-like anion, and M is antimony, arsenic or phosphorus, preferably employing an ammonium salt and carried out in a non-aqueous solvent.

DESCRIPTION

The present application is a Continuation-in-Part of co-pendingapplication Ser. No. 07/152,729 filed Feb. 5, 1988, now abandoned.

1. Technical Field

The present invention is concerned with an improved synthesis oftriarylsulfonium salts.

2. Background Art

Triarylsulfonium salts are used as photo-acid initiators forpolymerization and ester cleavage. They are also used as radicalphotoinitiators. They have, however, suffered from the disadvantage frombeing extremely expensive and also needing to be exceptionally pure whenthey are used.

The most commonly used synthesis of triarylsulfonium salts is that givenby Crivello and Lam, J. Polym. Sci., 17, 977 (1979). This method isusually called the "iodonium salt route". The method has thedisadvantage of requiring the use of toxic iodonium salts. It has theadditional disadvantage in that it is a two-step process and thatexpensive reagents are used in the lower yielding first step of thetwo-step process. The products from each step are impure, being isolatedas colored oils. Multiple recrystallizations are required in order toobtain white crystalline products.

The literature also describes another method for the synthesis oftriphenylsulfonium salts. This two-step process is described by thefollowing equations: ##STR1## wherein Ar is aromatic such as phenyl,tolyl, etc., X is a halogen such as bromide, and Z is a alkali metalsuch as sodium and M is antimony, arsenic or phosphorus. Step 1 of thissynthesis is described in Wildi et al, J. Amer. Chem. Soc., 73, 1965(1951) and LaRochelle et al, J. Amer. Chem Soc., 93, 6077 (1971). Step 2of this synthesis is described by Smith, U.S. Pat. No. 4,173,476. It iswith improvements in these synthetic methods that the present inventionis concerned.

DISCLOSURE OF THE INVENTION

The above-described process is greatly improved by certain changes inthe procedure. In the prior art, the Grignard reaction used either etheror ether-benzene co-solvents. According to the present invention,greatly higher yields are obtained using a solvent which is a mixture ofliquid aromatic and aliphatic hydrocarbons. Using the solvent mixture ofthe present invention also has the advantages of shorter reaction times,3 hours versus 18 hours in the prior art. Furthermore, less Grignardreagent can be used.

The present invention requires only 3 equivalents of Grignard reagent(Example 1) to give 60% yield of product, whereas the prior art requires5 equivalents of the reagent and gives less product, 39% laRochelle etal, 49% Wildi et al. For direct comparison, when 2 equivalents ofGrignard reagent are used, the present invention gives a 47% yield ofproduct (Example 6), whereas the prior art, Wildi et al, reports only14% yield of product. To demonstrate the necessity of the addition ofaliphatic hydrocarbon co-solvent, the same reaction as Example 6 was runusing 5 equivalents of Grignard reagent in benzene solvent and only 45%yield of product was obtained after 18 hours (Example 8). The aromaticco-solvent is not restricted to benzene; toluene (Example 7) cansatisfactorily be used.

In the prior art, the second step of the reaction was carried out usingaqueous solvents. This causes hydrolysis of the anion, givingundesirable side reactions and lower yields of product. We have nowfound that the procedure is greatly improved when a non-aqueous solventis used. Examples 9-17 demonstrate the use of non-aqueous ketone,nitrile, alcohol and ester solvents.

Furthermore, we have found that the throughput for the process isimproved when an ammonium salt is used for the metathetical second stepof the process (Example 11). Using the improved process of the presentinvention, the products of each of the two steps of the reactions arewhite crystals. The process also has the additional advantage in that,in the process of the present invention, the expensive MX₆ anion is usedin the high yielding second step.

The following Examples are given solely for the purposes of illustrationand should not be thought as limitations on the present invention, manyvariations of which are possible without departing from the spirit orscope thereof.

GRIGNARD REACTIONS Example 1

A 3.0 M solution of phenylmagnesium bromide in diethyl ether (50 ml,0.15 mole) was distilled under vacuum with slow heating from 20° to 80°C. Benzene (40 ml) was added, followed by n-heptane (300 ml). Theresulting mixture was stirred and a solution of diphenylsulfoxide 10.1g, (0.050 mol), in benzene (60 ml) was added during 1 hour at 80° C. Themixture was stirred for 3 hours and cooled to room temperature. An 25%aqueous hydrobromic acid solution (180 ml) was slowly added to thereaction mixture (exotherm-). The layers were separated and the organiclayer was extracted twice with 5% aqueous hydrobromic acid (2 x 30 ml).The combined aqueous extracts were extracted three times withdichloromethane (3×250 ml). The dichloromethane extracts were dried overmagnesium sulfate, filtered and the organic solvent evaporated to leavetriphenylsulfonium bromide (10.2 g, 60%), which was crystallized fromdichloromethane/diethyl ether. M.p. 285-7 ° C.

Example 2

A 3.0 M solution of phenylmagnesium bromide in diethyl ether (50 ml,0.15 mole) was distilled under vacuum with slow heating from 20° to 80°C. Benzene (40 ml) was added, followed by n-heptane (100 ml). Theresulting mixture was stirred and a solution of diphenylsulfoxide 10.1g, (0.050 mol), in benzene (60 ml) was added during 1 hour at 80° C. Themixture was stirred for 3 hours and cooled to room temperature. An 25%aqueous hydrobromic acid solution (180 ml) was slowly added to thereaction mixture (exotherm-). The layers were separated and the organiclayer was extracted twice with 5% aqueous hydrobromic acid (2 x 30 ml).The combined aqueous extracts were extracted three times withdichloromethane (3 x 250 ml). The dichloromethane extracts were driedover magnesium sulfate, filtered and the organic solvent evaporated toleave triphenylsulfonium bromide (10.0 g, 59%).

Examples 3-5

Bromobenzene (28.4 g, 0.181 mol) was added to a stirred mixture ofmagnesium (4.3 g, 0.177 mol) in diethyl ether during hour. The resultingmixture of phenylmagnesium bromide and diethyl ether was distilled undervacuum with slow heating from 20° to 80° C. Benzene (50 ml) was added,followed by n-heptane (375 ml). The resulting mixture was stirred and asolution of diphenylsulfoxide 12.1 g, (0.0598 mol, in benzene (75 ml)was added during 1 hour at 80° C. The mixture was stirred for 3 hoursand cooled to room temperature. An 25% aqueous hydrobromic acid solution(200 ml) was slowly added to the reaction mixture (exotherm-). Thelayers were separated and the organic layer was extracted twice with 5%aqueous hydrobromic acid (2 x 30 ml). The combined aqueous extracts wereextracted three times with dichloromethane (3 x 250 ml). Thedichloromethane extracts were dried over magnesium sulfate, filtered andthe organic solvent evaporated to leave triphenylsulfonium bromide (12.3g, 60%). Tris-(4-methylphenyl)sulfonium bromide andtris-(4-chlorophenyl)sulfonium bromide were prepared from theirrespective diarylsulfoxides and bromoarenes by the above procedure.

Example 6

A 3.0 M solution of phenylmagnesium bromide in diethyl ether (33 ml,0.10 mole) was distilled under vacuum with slow heating from 20° to 80°C. Benzene (40 ml) was added, followed by n-heptane (100 ml). Theresulting mixture was stirred and a solution of diphenylsulfoxide 10.1g, (0.050 mol), in benzene (60 ml) was added during 1 hour at 80° C. Themixture was stirred for 18 hours and cooled to room temperature. An 25%aqueous hydrobromic acid solution (180 ml) was slowly added to thereaction mixture (exotherm-). The layers were separated and the organiclayer was extracted twice with 5% aqueous hydrobromic acid (2 x 30 ml).The combined aqueous extracts were extracted three times withdichloromethane (3×250 ml). The dichloromethane extracts were dried overmagnesium sulfate, filtered and the organic solvent evaporated to leavea residue which was crystallized from dichloromethane/diethyl ether togive triphenylsulfonium bromide (8.1 g, 47%).

Example 7

A 3.0 M solution of phenylmagnesium bromide in diethyl ether (42 ml,0.126 mole) was distilled under vacuum with slow heating from 20° to 80°C. Toluene (40 ml) was added, followed by n-heptane (200 ml). Theresulting mixture was stirred and a solution of diphenylsulfoxide 10.1g, (0.050 mol), in benzene (60 ml) was added during 1 hour at 80° C. Themixture was stirred for 3 hours and cooled to room temperature. An 25%aqueous hydrobromic acid solution (180 ml) was slowly added to thereaction mixture (exotherm-). The layers were separated and the organiclayer was extracted twice with 5% aqueous hydrobromic acid (2×30 ml).The combined aqueous extracts were extracted three times withdichloromethane (3×250 ml). The dichloromethane extracts were dried overmagnesium sulfate, filtered and the organic solvent evaporated to leavea residue which was crystallized from dichloromethane/diethyl ether togive triphenylsulfonium bromide (7.7 g, 44%).

Example 8

A 3.0 M solution of phenylmagnesium bromide in diethyl ether (83 ml,0.25 mole) was distilled under vacuum with slow heating from 20° to 80°C. Benzene (140 ml) was added, the resulting mixture was stirred and asolution of diphenylsulfoxide 10.1 g, (0.050 mol), in benzene (60 ml)was added during 1 hour at 80° C. The mixture was stirred for 18 hoursand cooled to room temperature. An 25% aqueous hydrobromic acid solution(180 ml) was slowly added to the reaction mixture (exotherm-). Thelayers were separated and the organic layer was extracted twice with 5%aqueous hydrobromic acid (2×30 ml). The combined aqueous extracts wereextracted three times with dichloromethane (3×250 ml). Thedichloromethane extracts were dried over magnesium sulfate, filtered andthe organic solvent evaporated to leave triphenylsulfonium bromide (7.7g, 45%).

METATHESIS REACTIONS Example 9

Triphenylsulfonium bromide (50 g, 0.146 mole) and sodiumhexafluoroantimonate (38 g, 0.147 mole) were mixed in 300 ml of acetoneand stirred for 3 hr. The suspension was filtered and the filtrateevaporated to yield a white solid (72.0 g, 100%). Recrystallization fromethanol gave white needles m.p. 203-5° C.

Example 10

Triphenylsulfonium bromide (15 g, 0.0437 mole) and sodiumhexafluoroantimonate (11.3 g, 0.0437 mole) were mixed in 250 ml ofacetone and stirred for 3 hr. The suspension was filtered and thefiltrate evaporated to yield a white solid (21.8 g, 100%).Recrystallization from ethanol gave white needles.

Example 11

Triphenylsulfonium bromide (1.72 g, 5.01 mmole) and ammoniumhexafluorophosphate (0.82 g, 5.03 mmole) were mixed in 60 ml ofacetonitrile and stirred for 15 hr. The suspension was filtered and thefiltrate evaporated to yield a white solid (2.02 g, 99%).Recrystallization from ethanol gave white needles m.p. 178-9° C.

Example 12

Triphenylsulfonium bromide (1.72 g, 5.01 mmole) and potassiumhexafluorophosphate (1.38 g, 7.50 mmole) were mixed in 60 ml of acetoneand stirred for 15 hr. The suspension was filtered and the filtrateevaporated to yield a white solid (2.01g, 98%). Recrystallization fromethanol gave white needles.

Example 13

Triphenylsulfonium bromide (2.00 g, 5.83 mmole) and sodiumhexafluoroantimonate (1.50 g, 5.80 mmole) were mixed in 60 ml of acetoneand stirred for 5 hr. The suspension was filtered and the filtrateevaporated to yield a white solid (2.87g, 99%).

Example 14

Triphenylsulfonium bromide (0.50 g, 1.46 mmole) and sodiumhexafluoroantimonate (0.37 g, 1.43 mmole) were mixed in 60 ml ofethylacetate and stirred for 5 hr. The suspension was filtered and thefiltrate evaporated to yield a white solid (0.70g, 98%).

Example 15

Tris-(4-chlorophenyl)sulfonium bromide (0.85 g, 1.90 mmole) sodiumhexafluoroantimonate (0.493 g, 1.91 mmole were mixed in 30 ml of acetoneand stirred for 5 hr. The suspension was filtered and the filtrateevaporated to yield a white solid (1.13 g, 99%).

Example 16

Tris-(4-methylphenyl)sulfonium bromide (3.57 g, 9.26 mmole) and sodiumhexafluoroantimonate (2.58 g, 9.97 mmole) were mixed in 60 ml of acetoneand stirred for 5 hr. The suspension was filtered and the filtrateevaporated to yield a white solid (5.0g, 100%).

Example 17

Tris-(4-methylphenyl)sulfonium bromide (2.5 g, 6.49 mmole) and sodiumhexafluoroantimonate (1.68 g, 6.49 mmole) were mixed in 60 ml of acetoneand stirred for 5 hr. The suspension was filtered and the filtrateevaporated to yield a white solid (3.5g, 100%).

What is claimed is:
 1. A process for the synthesis of a triarylsulfoniumsalt in which each of the aryl radicals are the same and are eachselected from the group consisting of phenyl, methylphenyl, halophenyland unsubstituted hydrocarbon aryl, by the reaction of an aryl Grignardreagent with a diarylsulfoxide followed by a metathetical secondreaction with a compound of the formula ZMF₆ where Z is selected fromthe group consisting of alkali metal and ammonium ions and M is selectedfrom the group consisting of antimony, arsenic and phosphorus, whereinthe improvement comprises carrying out the first step of the reaction ina solvent which is a mixture of liquid aromatic and aliphatichydrocarbons.
 2. A process as claimed in claim 1 wherein the improvementalso comprises carrying out the metathetical second reaction in asolvent selected from the group consisting of ketone, nitrile, alcoholand ester solvents.
 3. A process as claimed in claim 1 wherein theimprovement also comprises using ammonium hexafluorophosphate in themetathetical reaction.
 4. A process as claimed in claim 1 wherein theimprovement also comprises using ammonium hexafluoroantimonate in themetathetical reaction.
 5. A process as claimed in claim 2 whereethylacetate is the solvent in the metathetical reaction.
 6. A processas claimed in claim 2 wherein acetone is the solvent in the metatheticalreaction
 7. A process as claimed in claim 2 wherein acetonitrile is thesolvent in the metathetical reaction.
 8. A process as claimed in claim 2wherein ethanol is the solvent in the metathetical reaction.